1. Field of the Invention
The present invention relates to an optical pickup for an optical recording/reproducing apparatus. More particularly, the present invention relates to an optical pickup that is capable of recording and/or reproducing information on various kinds of optical information recording mediums, such as compact discs (CDs), digital versatile discs (DVDs), advanced optical discs (AODs), blue-ray discs (BDs), and the like.
2. Description of the Related Art
Recently, short-wavelength red lasers have found a practical use in DVDs, which have a recording capacity substantially equal to or higher than that of CDs, and have come into widespread use.
A CD is an optical information recording medium that is adapted to record and/or reproduce information using light having a wavelength of 780 nm and an objective lens having a numerical aperture of 0.45 or 0.5. A DVD is an optical information recording medium adapted to record and/or reproduce information using light having a wavelength of 650 nm and an objective lens having a numerical aperture of 0.6 or 0.65. A DVD has a recording capacity of about 4.7 GB. A DVD can be called a high density optical information recording medium, as compared to a CD that has a recording capacity of about 0.65 GB.
As blue lasers that generate and project short-wavelength laser beams of about 400 nm have come into use, optical information recording mediums that allow the recording of information at a higher density have appeared. An AOD (Advanced Optical Disc), which is also called a next generation High-Definition DVD (HD-DVD), is an optical information recording medium that records and/or reproduces information using light having a wavelength of 405 nm and an objective lens having a numerical aperture which is the same as that used in a DVD. Such an AOD has a higher recording density as compared to a DVD because it uses short-wavelength light. In addition, it has an advantage over Blue-ray Disc (BD) technology because it uses an objective lens with the same NA as that used in a DVD, which provides a compatibility advantage.
A BD is an optical information recording medium that is adapted to record and/or reproduce information using light having a wavelength of 405 nm and an objective lens having a numerical aperture of 0.85, wherein the BD has a high recording density of about 25 GB. Recently, diverse research and development is being conducted on such a BD, which has been proposed as a high density optical information recording medium suitable for recording high definition moving image information.
As various types of high density optical recording mediums have been developed as described above, optical pickups have been developed which are compatible with both high density optical recording mediums and low density optical recording mediums. For convenience, the term “compatible optical pickup” will be used to refer to an optical pickup which is compatible with more than one type of recording medium.
Conventional compatible optical pickups typically employ two or three light sources to generate and project short-wavelength (405 nm) laser beams for use in a high density optical information recording medium and long-wavelength (655 nm and 785 nm) laser beams for use in a low density optical information recording medium, and two objective lenses each for use in a high density optical information recording medium and a low density optical information recording medium.
Such conventional compatible optical pickups may be compatible with a CD, a DVD and one of an AOD or a BD. An optical pickup, which is compatible with all four types of optical recording mediums, that is, AOD, BD, DVD and CD, has not yet been made available.
Accordingly, there is a need for a compatible optical pickup which is compatible with all of an AOD, a BD, a DVD and a CD.